1. Electrolysis
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Why do covalent compounds not conduct electricity?
• Most covalent compounds do not conduct electricity as they have no freely moving charged particles to carry the current • They act as insulators
What is a cation?
Positive ions
What is anion?
Negative ions
Why cant ionic compounds conduct electricity in the solid state?
They cannot conduct electricity in the solid state as the ions are in fixed positions within the lattice and are unable to move and carry a charge.
What is electrolysis?
Electrolysis is the breaking down of an ionic compound using electricty.
What will aluminum oxide break down into?
• Aluminum • Oxygen
Why is graphite used for the electrodes?
It is inert so wont react with the electrolyte solution.
What is the anode?
The positive electrode which attracts negative ions.
What is the cathode?
The negative electrode which attracts positive ions.
In aqueous solutions electrolysis what does water disassociate to?
H2O ⇌ H+ + OH–
What it produced at the cathode in electrolysis of aqueous solutions.
• Positively charged H+ and metal ions are attracted to the negative electrode but only one will gain electrons • Either hydrogen gas or the metal will be produced • If the metal is above hydrogen in the reactivity series, then hydrogen will be produced and bubbling will be seen at the cathode • This is because the more reactive ions will remain in solution, causing the least reactive ion to be discharged
What it produced at the anode in electrolysis of aqueous solutions.
• Negatively charged OH– ions and non-metal ions are attracted to the positive electrode • If halide ions (Cl-, Br-, I-) and OH- are present then the halide ion is discharged at the anode, loses electrons and forms a halogen (chlorine, bromine or iodine) • If no halide ions are present, then OH- is discharged at the anode, loses electrons and forms oxygen
OIL RIG
• Oxidation • Is • Loss of Electrons • Reduction • Is • Gain of electrons
Are ions at the anode oxidised or reduced?
At the anode, negatively charged ions lose electrons and are thus oxidised.
Are ions at the cathode oxidised or reduced?
At the cathode, the positively charged ions gain electrons and are thus reduced.
Water half - equation
2H2O ⟶ O2 + 4H+ + 4e–
What happens at the cathode in electrolysis of molten lead(II) bromide?
Pb²⁺ + 2e⁻ → Pb (reduction) Product: lead Colour: grey / silvery State: liquid (when hot and molten), solid when cooled
What happens at the anode in electrolysis of molten lead(II) bromide?
2Br⁻ → Br₂ + 2e⁻ (oxidation) Product: bromine Colour: red-brown State: gas
What happens at the cathode in electrolysis of aqueous sodium chloride?
2H⁺ + 2e⁻ → H₂ (reduction) Product: hydrogen Colour: colourless State: gas
What happens at the anode in electrolysis of aqueous sodium chloride?
2Cl⁻ → Cl₂ + 2e⁻ (oxidation) Product: chlorine Colour: pale green State: gas
What happens at the cathode in electrolysis of dilute sulfuric acid?
2H⁺ + 2e⁻ → H₂ (reduction) Product: hydrogen Colour: colourless State: gas
What happens at the anode in electrolysis of dilute sulfuric acid?
2H₂O → O₂ + 4H⁺ + 4e⁻ (oxidation) Product: oxygen Colour: colourless State: gas
What happens at the cathode in electrolysis of aqueous copper(II) sulfate?
Cu²⁺ + 2e⁻ → Cu (reduction) Product: copper Colour: pink-brown State: solid
What happens at the anode in electrolysis of aqueous copper(II) sulfate?
2H₂O → O₂ + 4H⁺ + 4e⁻ (oxidation) Product: oxygen Colour: colourless State: gas